Dry eye (DE), and one of its major forms - chronic posterior blepharitis (CPB) - is a widespread multifactorial disease that diminishes the quality of life of millions of people, especially elderly, women, and those who live in adverse climates, by impairing their vision. Up to 30% of the general population is affected by DE. No effective treatment for DE exists at present with the only FDA-approved drug for treating DE and CPB, Restasis(R), having a therapeutic effect in 15% of patients vs. 5% in the placebo group. The disease is linked to changes in the very thin lipid- and protein rich ocular surface structure called tear film (TF). The long-term goals of our project are: 1) to redefine the biochemical composition and 3-D structure of TF, and 2) to determine the major biochemical and biophysical factors that stabilize or destabilize TF and hence those components important for the development of CPB and DE in general. Our general hypotheses are that: 1) the lipid composition of TF is more elaborate than previously thought; 2) the TF structure is stabilized due to very specific lipid/lipid and lipid/protein interactions; and, 3) TF is not quite liquid but instead has either a liquid crystal-like, or a gel-like structure and is composed of gradually intercalating layers and zones enriched with particular types of molecules and supramolecular complexes. The aims of the project are as follows. Aim 1. To challenge the current views on the biochemical composition of human TF as formed primarily of MGS by comparatively characterizing the lipids of MGS and AT, determining the lipid components of TF and their likely sources, and identifying and evaluating the roles of the critical lipid components in the formation and maintaining of TF. Aim 2. To test the hypothesis that normal TF is not quite liquid but instead has an either liquid crystal-like or a gel- like dynamic nanostructure composed of gradually intercalating layers and zones enriched with particular types of molecules and supramolecular complexes which is stabilized by ionic and hydrophilic/hydrophobic interactions between lipids, proteins, and other molecules and whose structure is susceptible to changes due to alterations in its lipid and protein compositions, tear osmolality, ocular temperature, mixing, environmental factors, etc. Aim 3. To determine whether or not there are cyclic qualitative and quantitative changes in human AT lipids and MGS that could be associated with the cyclic increase of DE symptoms and TF instability in CPB patients compared with normal subjects.